Control unit



F. F. BAHNSON compor, UNIT Nov. 4, 1941,

Filed g. 2, 1959 2 Sheets-Sheet l Nov. 4, 1941.

F. F. BAHNSON I 2,261,750

CONTROL UNIT Filed Aug. 2, 1939 2 Sheets-Sheet 2 Patented Nov. 4, 1941 UNITED STATES PATENT OFFICE CONTROL UNIT Frederic F. Bahnson, Winston-Salem, N. (3., assignor to The Bahnson Company, Winston- Salem, N. C., a corporation of North Carolina Application August 2, 1939, Serial No. 288,027

6 Claims.

This invention relates to control units and particularly to control units of the type including an electrical switch actuated by a member that is affected by, and varies in length with, changes in a preselected condition of a fluid medium.

An object of the invention is to provide simple and reliable control units of high sensitivity that afford a close regulation of the preselected condition, which may be temperature or humidity, about the desired control point. An object is to provide control units of the type stated that in clude an electrical switch having a plunger, an elongated strip element that varies in length with temperature or humidity, a frame or support upon which the strip element is suspended in axial alinement with the switch plunger, and a spring-pressed link depending from the strip element for actuating the switch plunger. An object is to provide control units of the type last stated in which the strip element is suspended from the frame or supporting structure by threaded members that may be adjusted to determine the control point, temperature or humidity, at which the strip element actuates the switch. An object is to provide a control unit including a supporting structure having two vertically spaced plates, an elongated strip element suspended from the upper plate and carrying a tensioned link that projects through the lower plate, and a switch mounted on the supporting structure below the lower plate, the switch having a plunger in line with the tensioned link for actuation thereby and the strip element being adjustably supported on the upper plate to vary the effective length of the strip element and link.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawings in which:

Fig. 1 is a front elevation of a temperatureresponsive control device of the present invention, but with the outer casing removed;

Fig. 2 is a longitudinal section taken vertically and centrally of the device of Fig. 1;

Figs. 3 and 4 are plan views, top and bottom respectively, of the same device, with several of the parts removed in Fig. 3 for clarity of illustration;

Fig. 5 is an enlarged fragmentary sectional view on line 5--5 of Fig. 1, with suflicient parts removed to permit the initial adjustment of the control unit;

Fig. 6 is a fragmentary perspective view of the supporting bracket;

Fig. 7 is a perspective view of the closure and housing member that fits said bracket;

Fig. 8 is a fragmentary View, corresponding to the upper part of Fig. 1 but showing a modified form of control unit;

Fig. 9 is a section taken on line 99 of Fig. 8, with certain parts removed; and

Fig. 10 is a plan view looking down upon the top of Fig. 9.

As shown in Fig. 1, the control unit consists essentially of an elongated responsive element R tensioned between an adjustable upper anchorage A and a tensioning device T, the latter being anchored to or forming a part of a mounting device M and being fixedly separated from. the anchorage A by three or more rods I2. These rods preferably are formed of stainless steel or Invar so as to have substantially no variation in length as the temperature changes. The upper ends of the rods carry a cupped plate l3 and a thicker rigid plate I4 that are secured in place by screws l5, and a curved indicator plate It is also anchored to one of the rods. The lower ends of the rods 12 are threaded into the upper plate 41 of a bracket member and secure an in- Verted cupped plate I8 to the plate l1. Plate l8 has a central square aperture I9 which permits reciprocation but not rotation of a four-sided link 29 that is threaded at its lower end to receive a nut 22, and the upper end of the link being connected to the elongated strip element R by a screw and nut assembly 23. A compression spring 24 surrounds the link 20 to react between nut 22 and plate 18, the plate ll having a large aperture 25 to prevent interference with the spring action.

The strip element R comprises a pair of laterally spaced strips 26 of Dow metal, aluminum or other material that expands and contracts with changes in temperature and has the requisite tensile strength. The multiple strip construction permits the use of thin metal sheets of low heat inertia and, when an even number of strips is used, the axis of link 20 coincides with the axis of the strip element R. and the parts are subjected only to pure tension stresses. A nut and bolt 21 connect the upper ends of the metal strips 26 to a second square link 28 that extends through a square hole 29 in the upper domed plate l3. The upper threaded end of the link 28 passes freely through the bore of a bushing 30 that is secured to the plate l4, preferably by soldering the flange 3| of the bushing to the plate. The outer surface of the bushing 30 has somewhat coarser threads than those of the link 28, for example 20 threads per inch on bushing 30 and 25 threads per inch on the link 28. A sleeve 32 is threaded on the bushing and is counterbored from the top to receive the lower end of a cylindrical nut 33 that has a circumferential groove 34 for receiving the set screw 35 of the sleeve 32.

A bell shaped cap 36 is fitted over the upper threaded end of the nut 33 and is clamped in place by the nut 37 that has a central bore 38 through which a square-ended tool may be passed to enter the correspondingly shaped recess in "the nut 33. The nut 33 also has a milled edge 40 which facilitates the initial adjustment of the nut on the link 28. When the cap 36 is secured to the nut 33, the cap may be turned to adjust the effective length of the elongated control element. An indexing device is provided by the block or cylinder 4| that is soldered to the plate 14 and carries a plunger 42 which engages shallow corrugations 42a in the skirt of the cap 36, the plunger being pressed outwardly by a spring 43.

The electrical switch which is to be controlled by the strip element R. is preferably of the type described in the patent to Phillip K. McGall, No. 1,960,020, which is operable by a relatively small displacement of a small plunger. The switch is mounted in a one-piece bracket 44 that includes inclined walls 45 depending from the edges of the plate I! and terminating in parallel vertical walls 46. The walls 46 have alined openings 4! for receiving bolts 48 that clamp the rectangular switch unit 49 between the walls 46 to position the switch plunger 50 beneath and in axial alinement with the link 20. The exact details of the switch are not an important feature of this invention, the essential requirement being that the moving element of the switch snaps from one position to another upon depressing the plunger 50. The switch block carries appropriate terminals 52 for the switch contacts and the plate I! has an opening, provided with an insulating bushing 53, through which the leads may pass to the switch.

The bracket 44 has a vertical flange plate 54 provided with openings 55 for receiving screws or bolts to mount the bracket on a wall. A cover 56, see Fig. 7, comprises a U-shaped wall with a bent or channel upper edge 58 for fitting over the front and side edges of the plate IT, and a bottom wall 59 that terminates in a flange 60 which seats against the flange plate 54 of the mounting bracket and has an opening 62 in line with an opening 55 of the bracket. A sealing wire or look may be passed through the alined openings to prevent tampering with the switch and its leads.

The control unit is initially adjusted for operation at a preselected temperature range by assembling all parts except the domed cover 36 and its attaching nut 31. The unit is then brought to the midpoint of the temperature range of control, the set screw 35 is loosened and the nut 33 is slowly rotated until a clicking sound is heard as the switch is actuated. The direction of rotation to obtain this action can be determined by trial or by inspection of the link 20 and switch plunger 50. Set screw 35 is tightened to lock nut 33 to the sleeve 32. The cover is then placed on nut 33 with the zero mark of the cover in line with the center projection or flducial mark of the indicator plate l3. Nut 3'! is threaded upon the shank of nut 33, and a tool is inserted into the recess 40 of nut 33 to hold nut 33 while nut 31 is tightly threaded upon the stem of nut 33.

A perforated screen of conventional type, not shown, may be provided to enclose the space between the mounting bracket and the cover. This completes the assembly and calibration of the thermostatic control unit. Adjustment of cover 36 provides a regulation of the control point through a range at either side of the selected calibration point as the cover is now clamped to the sleeve 32 and nut 33. The differential threads in the devices for suspending the strip element provide a close and accurate regulation of the operating point for thermally responsive metal strips of relatively short length, for example four or five inches long.

Other types of control elements may be substituted in the general assembly of Figs. 1 and 2 when a condition other than temperature is to be regulated. As shown in Figs. 8 to 10, the upper link 65 is perforated to receive a cotter pin 66 by which the roller frame 51 is suspended from the link. The frame is the upper member of a hygroscopic control element such as shown in Fig. 1 of my prior Patent 1,954,911, granted April 17, 1934, and the active member of the control element is an elongated paper strip 68. The link 65 is threaded into a sleeve 69 that has threaded stem 10 on which nut 12 is seated to clamp the domed cover 13 to the sleeve. The upper end of the sleeve 69 has a non-circular bore and the nut 12 is hollow to permit the insertion of a tool into the sleeve 69 to hold it while turning the nut 12 down upon the stem 10.

The hygroscopic control unit is assembled and adjusted in the manner previously described with reference to the thermostatic unit. The differential thread construction could be employed in the hygroscopic control unit but, in general, the simpler construction of Fig. 9 affords a satisfactory regulation of the operating point.

The adaptability of the basic supporting structure to different control elements has the manufacturing advantage of economy in stock parts that may be assembled to provide various types of control units. The control units respond quickly to small changes in temperature or humidity as the variable-length control elements are of thin strip material that have but little inertia. Positive operation of the switch plunger is effected by the spring 24 which tensions the control element and thus eliminates slack from the system.

The illustrated control units constitute typical and preferred embodiments of the invention but it is to be understood that various changes may be made in the shape, size and relative arrangement of the parts without departing from the spirit of my invention as set forth in the following claims.

I claim:

1. In a control unit, a supporting structure comprising a pair of plates and means securing the same in fixed parallel relation, said plates having openings in alinement, an elongated variable length control element between said plates, links of non-circular cross-section connected to opposite ends of said control element and'slidably extending through the openings in the respective plates, means preventing rotation of said links, means for anchoring one link to one of said plates, means associated with the other plate for tensioning said control element, a control device having an actuating plunger, and means securing said control device to said second plate with the plunger in line with the adjacent link; said anchoring means including a nut threaded upon the associated link, a domed cover adjustably secured to said nut and carrying graduations extending in opposite directions from a zero mark, and an indicator strip carried by the adjacent plate and having a fiducial mark.

2. A control unit comprising a bracket including a plate having an opening therethrough and supporting means below said plate, a control device including an operating plunger, means mounting said control device on said supporting means with the plunger in line with the opening in the plate, a second apertured plate, rods supporting said second plate above said bracket and parallel to the first plate, links of non-circular cross-section slidably extending in axial alinement through the openings in the respective plates, a nut threaded upon the upper link above the second plate, a guide plate secured to the second plate and having a non-circular opening through which the associated link extends, an elongated control member connected between said links, an inverted domed plate on the upper face of the bracket plate and having a non-circular guide opening for the lower link, and spring means between said domed plate and the lower link for tensioning said control member, the lower link being in axial alinement with the plunger.

3. The invention as claimed in claim 2, in combination with a domed cover secured to said nut and having a flange terminating adjacent the second plate, and cooperating indicating means carried respectively by said domed cover and said second plate.

4. The invention as claimed in claim 2, in combination with a threaded bushing secured to the upper surface of the second plate, a sleeve threaded upon said bushing and secured to said nut, the pitch of the threads of said bushing and said nut being different, whereby rotation of said nut and sleeve affords a slow-motion adjustment of the upper link with respect to the upper plate of said supporting structure.

5. In a control unit, the combination with a bracket comprising a plate having parallel walls below and integral with the opposite edges of the plate, and a mounting wall depending below one end of the plate, said plate having an opening therethrough, of a control device supported by said parallel walls, said control device having an axially movable operating plunger in line with the opening in the plate, an upper apertured plate and parallel rods supporting the same upon and in spaced parallel relation to the bracket plate, an elongated control element having the ends thereof slidably extending through the openings in said plates, means anchoring the upper end of the control element to the upper plate, and spring means at the bracket plate for maintaining said control element under tension, the lower end of said control element being alined with the plunger.

6. The invention as claimed in claim 5, wherein said anchoring means includes a nut threaded upon the control element, a domed cover secured to said nut and enclosing the nut and the upper plate, and indicator means carried respectively by said domed cover and said apertured plate to indicate adjustments of the control point of said control unit.

FREDERIC F. BAHNSON. 

